This invention relates to an apparatus for measuring a moving state of a vehicle in a tunnel, in which by processing an image output signal from an image pickup camera installed in the tunnel, necessary traffic information such as velocity of a vehicle, the number of vehicles which have passed, distinction between a large vehicle and a small vehicle, and the like is measured and collected.
A conventional apparatus for measuring a moving state of vehicle or automobile in a tunnel is constructed in a manner such that original image data obtained by photographing a moving state of a vehicle in the tunnel and background data are image-processed to measure vehicle velocity, number of vehicles which have passed, kinds of vehicles (distinction between small car and large car), and the like, and the measured results are output.
In the above apparatus, the moving state of a vehicle is measured by a procedure shown in FIGS. 9A and 9B. FIG. 9A shows the conventional apparatus, while FIG. 9B illustrates the signal waveforms corresponding to each element of FIG. 9A.
A moving state of vehicle in a tunnel is photographed by a video camera 1 and a video analog signal is converted into digital data by an A/D converting section 2. The digital data i of one frame which has been converted by the A/D converting section 2 is stored into an image memory 3 together with background data ii previously stored as an image in the tunnel in a state in which no vehicle exists.
In an image processing section 4, data of the vehicle portion is extracted by a differential process (i-ii) between the digital data i and ii. By determining a portion of the data exceeding a threshold value, the front edge portion of the vehicle is detected.
The data of the front edge portion is sent to a data processing section 5. The data processing section 5 compares transmitted present data iii and previous data iv of the front edge portion which has been detected from the image before a predetermined time, thereby measuring the vehicle velocity, the number of vehicles passed, and the like. In these technical fields, for example, JP-A-2-306399 shows techniques for imaging or recording running vehicles by a TV camera, and JP-A-2-110695 shows a traffic control system for informing of escape directions upon occurrence of emergency states in a tunnel.
However, an illuminating apparatus in the tunnel has its illumination brightness changed between a few patterns in accordance with a brightness/darkness signal from a central unit, in order to reduce a difference between the brightness tunnel and the brightness in the outside the tunnel. In such a conventional apparatus for measuring a moving state of a vehicle in the tunnel, the video signal which is transmitted from the video camera changes at a time point at which the brightness in the tunnel is switched, so that differential data between the front edge data and the background data also changes and there is a possibility such that an error occurs in the data of the detected front edge portion. Therefore, the conventional apparatus for measuring the moving state of vehicle in the tunnel has a problem such that a measuring rate or capability of the traffic information deteriorates for a period of time which is taken until the measuring apparatus follows changes in brightness.